The use of a hand operated pointing device for use with a computer and its display has become almost universal. By far the most popular of the various devices is the conventional (mechanical) mouse, used in conjunction with a cooperating mouse pad. Centrally located within the bottom surface of the mouse is a hole through which a portion of the underside of a rubber-surfaced steel ball extends. The mouse pad is typically a closed cell foam rubber pad covered with a suitable fabric. Low friction pads on the bottom surface of the mouse slide easily over the fabric, but the rubber ball does not skid. Rather, the rubber ball rolls over the fabric as the mouse is moved. Interior to the mouse are rollers, or wheels, that contact the ball at its equator and convert its rotation into electrical signals representing orthogonal components of mouse motion. These electrical signals are coupled to a computer, where software responds to the signals to change by a ΔX and a ΔY the displayed position of a pointer (cursor) in accordance with movement of the mouse. The user moves the mouse as necessary to get the displayed pointer to a desired location or position. Once the pointer on the screen points at an object or location of interest, a button on the mouse is activated with the fingers of the hand holding the mouse. The activation serves as an instruction to take some action, the nature of which is defined by software in the computer.
A “track ball” is another example of a mechanical type of pointing device. A track ball is essentially an upside-down mouse. In a track ball, rather than sliding the device itself over a surface to produce pointer movement as in a mouse, a user directly contacts the mechanical ball with the user's finger, and causes the ball to rotate. As with a mouse, the movement of the mechanical ball in a track ball generates a corresponding movement of the displayed pointer.
In a track ball, the mechanical ball can be “flicked” with the finger, and the ball will continue to rotate under its own momentum after the user's finger is removed from the ball. The rotation continues until the user contacts the mechanical ball again, or until frictional forces eventually cause the ball to stop rotating. The inertial properties of a track ball that allow it to continue to generate pointer movement after the user stops contacting the mechanical ball result in good dynamic range. Small hand movements can result in large pointer movements. The inertial properties of a track ball are useful in some applications, such as game applications, where large and quick pointer movements are sometimes desirable. However, trackballs are not typically incorporated into modern laptop computers because such computers are designed to use more planar pointing devices, and the height of a typical trackball makes it incompatible with most laptop computers.
Some mechanical mouse devices may also provide inertial effects like a track ball. A mechanical mouse may be moved quickly over the mouse pad, and then lifted from the pad, allowing the ball to continue to rotate under its own momentum. Some mechanical mouse devices, however, cause the ball to immediately stop movement when the mouse is lifted from the mouse pad.
Conventional touchpads found on many laptop computers do not use a mechanical ball, or other similar moving mechanical element that has inertial properties. Touchpads are essentially writing surfaces that capture the position of a pointing object, such as a finger, pen, or stylus, which is moved across the writing surface. With a touchpad, position information is typically determined by sensing changes in resistance or capacitance. Touchpads are incorporated into many modern laptop computers because, unlike a trackball, touchpads are more planar, and have a size that permits easier incorporation into a laptop computer. Unfortunately, existing touchpads do not have much finesse, and several swipes across the touchpad surface must typically be performed to move the screen pointer to a desired location. It would be desirable in some applications for a touchpad to provide inertial effects, such as that provided by a track ball.